Metal oxide or metal oxynitride thin film transistors have many advantages such as a higher carrier density and higher mobility. Accordingly, the metal oxide or metal oxynitride thin film transistors can be made smaller, and the display panel made of such thin film transistors can achieve a higher resolution and a better display effect. Moreover, the metal oxide or metal oxynitride thin film transistors have the advantages of lower manufacturing costs, higher transmittance, and higher bad gap. The metal oxide or metal oxynitride thin film transistors have found a wide range of applications in display field.